1. Field of the Invention
The present invention relates generally to a method for estimating indicated mean effective pressure on each cylinder of an internal combustion engine for each firing attempt.
2. Background of the Invention
Computational methods to estimate the power produced in each cylinder of an engine have been developed, as described in U.S. Pat. No. 6,223,120. The inventors of '120 have disclosed a technique in which, based on the torsional characteristics of the engine and a measure of engine speed sampled at high bandwidth, the power produced in each cylinder can be computed. Such information can be used to determine a cylinder providing more or less power than the others. The inventors of the present invention have recognized disadvantages in this prior approach because the technique, disclosed in '120, computes engine power in each cylinder, but not instantaneously. Instead, the method of '120 requires sampling over a considerable period of time to obtain a reliable measurement. Thus, '120 appears to provide a measure of engine power in the cylinder only under steady speed conditions and recurring conditions. The inventors of the present invention have recognized that an intermittent condition, such as an occasional misfire, may not be detected using the method described in '120. The method in '120 is suitable for engines operating at steady conditions, such as power generating engines or pumping station engines, but is not well suited for automobile engines in which engine speed changes regularly. Another disadvantage is that the method in '120 involves Fourier analysis, which would tax onboard engine computers as this type of analysis is computationally intensive.